1. Field of the Invention
This invention generally relates to an offset rotary printing press having at least one printing stand with a plate cylinder, an inking unit for providing ink to the plate cylinder, a blanket cylinder, an impression cylinder, a sheet feed device for feeding printing stock into the print stand, and a dampening unit for feeding dampening medium to the printing plate of the plate cylinder. More specifically, the present invention relates to a dampening unit for an offset printing machine, which dampening unit can preferably have at least one forme roller that is engageable with the plate cylinder, a dipping roller dipping into dampening medium contained within a dampening-medium tank, at least one intermediate roller provided between the forme roller and the dipping roller, and adjusting means, by means of which the forme roller can be engageable with the plate cylinder and by means of which the intermediate roller can be engageable with the forme roller. At the dipping roller, the forme roller can preferably be pivot-mounted, and an additional connecting device can be provided between the forme roller and the intermediate roller to interconnect the forme roller and the intermediate roller.
2. Background Information
German Patent DE 31 46 223 C2 discloses one type of dampening unit for use in high-performance machines in which the dampening rollers involved may assume different positions. In this case, rollers having respective elastic outer cylindrical surfaces, called "blanket rollers", always cooperate with distributor rollers or intermediate rollers featuring respective rigid outer cylindrical surfaces. As such, if a printing machine is out of operation for several days, e.g. over the weekend, and contact pressure is left on between the blanket roller and, for example, a distributor roller, the contact pressure existing between the rollers may lead to a permanent deformation on the elastic outer cylindrical surface of the blanket roller. Once such a deformation has occurred, the deformation can typically only be eliminated after a rather long period of machine operation. In the area of the deformation of the outer cylindrical surface, the transfer of the thin dampening-medium film is affected, and the supply of dampening-medium to the printing plate may then fluctuate.